Automatic boiler blowdown



y 12, 1964 A. FJHOLMAN ETAL 3,132,631

AUTOMATIC BOILER BLOWDOWN Filed March 28, 1961 I5 Sheets-Sheet 1 INVENTORS ALVIN E HOLMAN DAV/D W SCOTT CMRLES 6'. STOKES M y 1 1964 A. F. HOLMAN ETAL AUTOMATIC BOILER BLOWDOWN Filed March 28, 1961 s Sheets-Sheei 2 I 1 &

k mill em "'4" s a Q o INVENTORS ssvw zw CHA Russ 6.5TOKES BY THEIR AT TQRNEY M y 12, 1954 A. F. HOLMAN ETAL 3,132,631

AUTOMATIC BOILER BLOWDOWN Filed March 28, 1961 3 Sheets-Sheet 3 FIG.3

INVENTORS ALVIN G. HOLMAN DAVID W. SCOTT CHARLES G. STOKES ATTORNEY United States Patent 3,132,631 AUTOMATIC BOILER BLOWDOWN Alvin F. Holman, 118 W. 8th St., Dallas, Tex., and David W. Scott and Charles G. Stokes, Dallas, Tex.; said Scott and said Stokes assignors to said Holman Filed Mar. 28, 1961, Ser. No. 98,345 9 Claims. (Cl. 122-382) The present invention relates to boiler blowdown systems and more particularly to a system that provides an automatic blowdown operation for all types of boilers.

If mud, scale, and other foreign materials are allowed to accumulate in a boiler, the boiler will be damaged and in some instances the damage may be extensive enough to render the boiler unsafe. It is common to blow down the boiler at certain intervals in order to keep the concentration of such foreign substances at a level that will not damage the boiler.

The American Society. of Mechanical Engineers has published what is generally referred to as the ASME Boiler and Pressure Vessel Code. Section 1, paragraph P-311A, of this code is cooncerned with the blow down of boilers. This code provides, among other things, that a blowdown pipe shall be located at the lowest point of the boiler that contains water. The code also provides that if the boiler is operated at a pressure in excess of 100 pounds per square inch (other than portable type boilers) at least two slow opening valves or one slow opening valve and one quick opening valve shall be placed in series in the blowdown line. This code has been incorporated into many state statutes.

As mentioned above, the blowdown operation is performed to purge the boiler of at least a portion of the mud, scale, and other foreign materials that may accumulate in the boiler due to the evaporation of water and thus prevent damage to the boiler and the creation of unsafe conditions. However, even if a blow down pipe and appropriate valves are provided, in many instances operators will fail to blow down the boiler at the necessary intervals. In some instances it is necessary to blow down the boiler as often as every 30 minutes. In other instances it may be necessary to blow down the boiler only once or twice a day. The frequency at which the boiler must be blown down will depend upon the type of service and the amount of return water that is used.

The present invention provides an automatic boiler blowdown system which alows the blowdown of boilers to be accomplished automatically without dependance upon action by the operator. Provision is made to protect against unwanted drainage of the boiler and the requirements of the ASME Boiler and Pressure Vessel Code as to the types of valves to be used in a boiler blowdown system are complied with.

In accordance with the present invention, a timer is utilized to initiate the blowdown operation at the desired times. A plurality of time delay electrical relays con trol the blowdown cycle by controlling the sequence oi operation of solenoid operated valves in a hydraulic system. A fail safe operation that protects the boiler against unwanted drainage is provided in which the blowdown cycle will stop and the blowdown line is closed in the event of power failure, either electrical or hydraulic, during the blowdown cycle. An alarm is also provided to warn the operators that the blowdown operation is commencing. Failure of the alarm to sound will indicate to the operator that the blowdown operation did not begin at the proper time.

It is therefore one object of this invention to provide a system that will automatically blow down a boiler at the desired time intervals.

Still another object of this invention is to provide a blowdown system capable of automatic operation that will prevent drainage of the boiler in the event of power failure.

These and many other objects of the present invention will become more readily apparent as the following detailed description of the preferred embodiment of the invention unfolds when taken in conjunction with the accompanying drawings wherein like reference numerals denote like parts and in which:

FIGURE 1 is a front elevation View showing the arrangement of the component parts of the boiler blowdown system according to one embodiment of the present invention;

FIGURE 2 is a schematic diagram illustrating the hydraulic system according to the preferred embodiment of the present invention;

FIGURE 3 is a schematic diagram showing an electrical control network according to the preferred embodiment of the present invention.

Turning now to the drawings and more particularly FIGURE 1 of the drawings, the automatic boiler blowdown system of the present invention is illustrated. As shown, the pipe 11 is connected to the lowest portion of the boiler 11 with which the blowdown system is to be associated. If a multiple drum system is used, the pipe Ill will be connected to the lowest portion of the mud drum. The blowdown products will pass through the blowdown line in the direction shown by the arrows and exit at the pipe 12 which may be connected to a tank or any other suitable means for disposing of the blowdown products. The actual flow of the blowdown products through the pipes Ill and 12 is controlled by a slow opening valve 14 and a quick opening valve 16. The slow opening valve 14 and the quick opening valve 16 are connected by a section of pipe 18.

In operation, a timer Zll energizes the electrical control circuit (to be described in greater detail in reference to FIGURE 3) at any predetermined time. In general, the control circuit comprises a two pole relay 22, three time delay relays 23, 24, and 25, a pressure sensitive switch 49, a pair of limit switches 86 and 9d, a. three-way solenoid operated valve 26, and a four-way solenoid operated valve 28. For clarity, electrical connections between the control elements are not shown in FIGURE 1.

The hydraulic system itself is illustrated in FIGURE 1, but perhaps best understood by reference to FIGURE 2. As shown in FIGURES l and 2, a hydraulic pump 31) is shown connected by pipe 32 to a reservoir 34. The hydraulic pump 30 can be driven by any suitable means such as an electric motor. The output of the pump 30 is connected via pipe 36 to a junction 38. From the junction 38, a portion of the hydraulic fluid being pumped flows through pipe 46 to a fiow control valve 42 and thence to the input of the four-way solenoid operated valve 28 via pipe 44. Pipe 46 connects one port of the four-way valve 28 to one port of the hydraulic motor 48. A pressure switch 49 is placed in this line. The hydraulic motor 48 is of the reversible type and functions to open and close the slow acting valve 14 by an axle and gear arrangement 58. As the valve 14 is opened by the hydraulic motor 48, a projection on the shaft of the valve will bear against the nonnally open limit switch 86 causing the limit switch 86 to close when the valve 14 is in its completely open position. The other port of the motor 48 is connected by pipe 52 back to the four-way valve 28. The fourth port in the four-way valve 28 is connected through pipe 54 to the reservoir 34.

That portion of the hydraulic fluid not utilized by the hydraulic motor 48 is fed from the junction 38 through pipe 56 to a second flow control valve 58. The flow control valve 58 is connected to a check valve 64 by line 62. The hydraulic fluid passing through the check valve 64 flows to the three-Way solenoid operated valve 26 through pipe 66. One port of the three-way valve 26 is connected by pipe 70 to the hydraulic cylinder 72 which operates the fast opening valve 16. The large spring 74 biases the fast acting valve 16 in a normally closed position. Hydraulic pressure applied to the hydraulic cylinder 72 will open the valve 16 against the pressure of spring '74 and close the normally open limit switch 90. When the hydraulic pressure is released, the spring 74 will force the hydraulic fluid out of the cylinder 72 and close the quick acting valve 16. The third port of the three-way valve 26 is connected by a pipe 76 to the reservoir 34 thereby providing a closed hydraulic system. Safety valve 73 is connected to pipe 56 by pipe 77. The safety valve 78 provides an escape path for fluid to the reservoir 34 through the line 79 in the event pressure in the system exceeds a desirably safe limit.

The solenoid operated three-way valve 26 and the solenoid operated four-way valve 28 are the type that is well known in the art. When the solenoid on the three-way valve 26 is actuated a passage is provided for the flow of hydraulic fluid from line 66 to line 76 and the hydraulic cylinder 72. When the solenoid operator on the threeway valve 26 is not actuated, the valve allows the passage of fluid in a direction from line 70 through line 76 to the hydraulic reservoir 34.

The four-Way valve 28 will normally utilize a pair of oppositely disposed coils for actuating the valve. The arrangement of the coils is, of course, not critical. When the four-way valve 28 is not actuated, no fluid will flow through the lines 46 and 52. When the up solenoid is energized, the plug of the valve 23 will be positioned such that the flow of hydraulic fluid will be from line 44 into line 52, through the motor 48 and then returned to the valve 28 by line 46 which communicates with the exhaust port of the valve 28. The exhaust port of valve 28 is connected by line 54 to the reservoir 34. With the fluid flowing in this direction, motor 48 will rotate in a direction to produce rotation of the stem of the slow opening valve 14 in a direction causing the slow opening valve 14 to open.

On the other hand, when the down solenoid is energized, the line 46 will communicate with the line 44 and the line 52 will communicate with the exhaust line 54 causing the motor 48 to rotate in the opposite direction and drive the stem of the valve 14 in a direction to close it. As the valve 14 closes and seats itself the motor 48 will be unable to turn further and the pressure in the line 46 will increase very quickly due to the incompressibility of fluids. The increase of pressure in the line 46 will cause the normally open pressure sensitive switch 49 to close.

Turning now to FIGURE 3 of the drawings, the electrical control circuit will now be described in greater detail. A source of power such as the normally available 110 volts A.C. is connected to terminal C of the timer 20. The timer 20 is of conventional type and includes a switch for a predetermined time interval which closes at the time set for the blowdown cycle to begin. When the switch of the timer 20 closes, the contact C of timer 20 will be connected to the contact D of the timer 20.

A conductive lead 100 connects one side of the coil of Delayed Opening Relay 24, contacts E and F of Delayed Opening Relay 24 and contact B of relay 22 to terminal D of the timer 20. Terminal D of the timer 20 is also connected by line 102 to contact F of Delayed Opening Relay 23 and to one side of the coil of Delayed Opening Relay 23.

The other side of the coil of Delayed Opening Relay 24 is connected to ground through normally open limit switch 86. As mentioned earlier, the limit switch 86 is closed by the opening of the valve 14. In similar fashion, the other side of the coil of Delayed Opening Relay 23 is connected to ground through the normally open pressure switch 49 which closes momentarily on the closing of the slow opening valve 14. Therefore, Delayed Opening Relay 24 cannot become energized until the switch 86 closes,

4 and Delayed Opening Relay 23 cannot be energized until switch 49 closes.

One side of the alarm 82 is connected to ground. The other side of the alarm 82 is connected to contact B of Delayed Opening Relay 23 by line 104. The coil of the three-way solenoid operated valve 26 is also connected to ground and to contact B of Delayed Opening Relay 23 through line 104. The alarm 82 and the solenoid of the valve 26 will be actuated when the timer switch closes through the normally closed contact B and will remain actuated until the switch 49 closes, at which time the Delayed Opening Relay will be energized and the contact B will open.

Contact E of Delayed Opening Relay 23 is connected to contact B of Timed to Close Relay 25 by line 106. Contact A of Delayed Opening Relay 23 is connected to contact A of relay 22 by line 110. One side of the pump 30 is also connected to line 110, its other side being grounded. The pump 30 will begin to run when the relay 22 is energized to close contacts A and B of relay 22.

Contact B of relay 22 is also connected to one side of the up solenoid 92 through normally open limit switch 94). The other side of the up solenoid 92 is connected to terminal D of relay 22 by line 112. Contact C of relay 22 and one side of the coil of relay 22 are each connected to ground. The up solenoid 92 can be energized to control the four-way valve 28 to cause hydraulic fluid to flow through the motor 48 in a direction to open the slow opening valve 14 only when limit switch 99 is closed to permit power to be applied and, simultaneously, the relay 22 is energized provide a connection to ground through contacts C and D.

The other side of relay 22 is connected to contract A of Delayed Opening Relay 24 through line 114. Power is applied to the coil of relay 22 at all times when Delayed Opening Relay 24 is de-energized through normally closed contacts A and E, contact E being connected directly to line 1th).

Contact A of Timed to Close Relay 25 and one side of the coil of Timed to Close Relay 25 are connected to normally open contact C of Delayed Opening Relay 24 by line 116. One side of the down solenoid 84 is connected by line 113 to normally open contact D of Delayed Opening Relay 24. As the other side of the coil of Timed to Close Relay 25 and the other side of the down solenoid 84 are each connected to ground, the Timed to Close Relay 25 and the solenoid 84 will be energized when Delayed Opening Relay 24 is actuated by the closure of switch 86.

The operation of the automatic blowdown system of the present invention will now be described. At the instant the timer 20 energizes the electrical control circuit, power is supplied to the alarm 82, the coil 27 of the three-way solenoid valve 26, to one side of the coil of Delayed Opening Relay 23, to contact A of relay 22, to one side of the coil of Delayed Opening Relay 24 and to one side of the coil of Delayed Opening Relay 23. The other side of each of the alarm 82, the coil of the threeway solenoid operated valve 26 and the coil of relay 22 are connected to ground. Therefore, at the instant that the timer 2t energizes the control circuit, the alarm 82 will begin to sound, the three-way solenoid operated valve 26 will be operated to provide a conduit between line 66 and line 76 of the hydraulic system and the relay 22 will be energized. When the relay 22 is energized, power will be applied through contacts A and B of relay 22 to the ungrounded side of the pump 30, and the pump 30 will begin to build up pressure in the hydraulic system.

The pressure built up by the pump 30 is directed by the three-way valve 26 through line to the hydraulic cylinder 72 which immediately opens the quick acting valve 16 against the pressure of the spring 74. The check valve 64 placed on the pump side of the three-way valve 26 maintains the quick acting valve 16 open so long as the three-way solenoid operated valve 26 is energized. If

the check valve 64 is not provided, the spring 74 may close the valve 16 as the pressure decreases when the hydraulic motor 48 begins to run.

The opening of the quick opening valve 16 causes the normally opened limit switch 90 to close. When the limit switch 90 closes, it energizes the up solenoid 92 (through a ground provided by contacts C and D of relay 22) on the four-way valve 28. When the up solenoid 92 is energized, the plug of valve 28 is positioned to provide a conduit between lines 44 and 52 and between lines 46 and 54. The hydraulic fluid driven by pump 30 will flow through the hydraulic motor 48 in a direction to drive the axle and gear arrangement 50 to open the slow opening valve 14.

When the slow opening valve 14 is open the desired amount, itcloses a second normally opened limit switch 86. The closing of limit switch 86 allows the Delayed Opening Relay 24 to be energized. Delayed Opening Relay 24 breaks the circuit to the coil of relay 22 when it actuates by breaking the connection between contact A and E of Delayed Opening Relay 24. As relay 22 returns to the de-energized position, it removes power from the pump 30 and removes the ground from the up solenoid 92. The pump 30 will cease to operate and the valve 28 will close, thereby stopping hydraulic motor 48. At the same time, the closure of contacts C and E of Delayed Opening Relay 24 energizes the coil of Timed To Close Relay 25. The closure of contacts D and F of Delayed Opening Relay 24 energizes the down solenoid 84 of valve 34 providing communication between lines 44 and 46 and between lines 52 and 54. The motor 48, however, will not turn as the pump 30 is inoperative. The Delayed Opening Relay 24 is maintained in the actuated position by its time delay until the timer 20 de-energizes the entire control circuit thereby insuring that the up solenoid 92 of valve 28 does not subsequently become energized.

The Timed to Close Relay 25, then, after a predetermined time delay, closes and applies power to the pump 30. This time delay is the effective blowdown period of the system. As pump 30 operates, it causes the hydraulic fluid to flow through the four-way valve such as to route the hydraulic fluid through the reversible hydraulic motor in a direction to close the slow opening valve 14. A normally openpressure switch 49 is located in the line 46 that serves as the inlet to the hydraulic motor 48 on the down cycle. When the valve stem of the slow acting valve 14 seats itself in the lowest possible position, the oil pressure driving the hydraulic motor 48 will rise rapidly because the motor will cease to turn restricting the flow of the hydraulic fluid. This rapid pressure rise causes the pressure switch 49 to be actuated and close its normally opened contacts. As the contacts of the normally opened pressure switch 49 close, a ground is provided to energize the Delayed Opening Relay 23. The Delayed Opening Relay 23 is quick to close but slow to open. When the Delayed Opening Relay 23 is energized, it removes power from the pump 30, the solenoid on the valve 26, and from the alarm 82. When the pump 30 stops, the pressure switch 49 will open causing the Delayed Opening Relay 23 to be de-energized. However, the time delay in Delayed Opening Relay 23 will cause its contacts to remain in the actuated position until after the timer 20 de-energizes the system. The actuation of Delayed Opening Relay 23 .will thus cause the alarm 82 to quit ringing and allow the solenoid on the three-way valve 26 to return to its original position causing the three-way valve 26 to route the hydraulic fluid directly from the hydraulic cylinder 72 on the quick opening valve 16 to the oil reservoir 34. The spring 74 mounted on the quick opening valve 16 immediately closes the valve 16 forcing all of the hydraulic fluid out of the cylinder 72. The delay in opening of Delayed Opening Relay 23 prevents the alarm 82 and the coil of solenoid operated 3-way valve 26 being reactuated before contacts C and D of timer 20 open.

From the above description, it is evident that the check valve 64 will maintain pressure on the cylinder 72 only as long as the three-way valve 26 remains energized as a direct path is provided through the three-way valve from the cylinder 72 to the reservoir 34 when the solenoid of the three-way valve 26 is de-energized. Therefore, if electrical power should ever fail during the operating cycle of the automatic blowdown system, the three-way valve 26 would be tie-energized and the heavy spring 74 would return the quick opening valve 16 to its normally closed position, thereby preventing unwanted drainage of the boiler. The slow opening valve 14 would, of course, remain in the position it occupied at the time of the power failure. When the power was again restored, the threeway valve would be energized causing the quick opening valve 16 to again open and the system would then complete its cycle from that point of the automatic blowdown cycle obtained at the time of the power failure.

Although the invention has been described with regard to one particular preferred embodiment, many changes and modifications of this preferred embodiment would be obvious to those skilled in the art. The invention is to be limited notto what has been disclosed herein, but only by the scope of the appended claims.

What ave claim is:

1. An automatic boiler blowdown system comprising a slow opening valve, a quick opening valve, means connecting said quick opening valve and said slow opening valve in series in the blow down line of the boiler, means biasing said quick opening valve in a norm-ally closed position, a hydraulic system effective to open said slow opening valve and said quick opening valve, control means for controlling the operation "of said hydraulic system to sequentially open and close said quick opening valve and said slow opening valve, and timer means for periodically actuating said control means.

2. An automatic boiler blowdown system comprising a slow opening valve, a quick opening valve, means connecting said quick opening valve and said slow opening valve in series in the blow down line of a boiler, a hydraulic motor for opening said slow opening valve, a four-way solenoid operated valve for "controlling the operation of said hydraulic motor to open and close said slow opening valve, a hydraulic cylinder adapted to open said quick opening valve, a solenoid operated three way valve for controlling the operation of said hydraulic cylinder to open said quick opening valve, means for maintaining the pressure in said hydrauliccylinder while said three- Way valve isactuated, means including a timer and a plurality of electrical relays for controlling the operation of said solenoid operated valves to sequentially open and close said slow opening valve and said quick opening valve, and means biasing said quick opening valve in a closed position efiective to close said quick opening valve when said solenoid operated three-way valve is de-actuated.

3. A system defined in claim 2 further including means for controlling the flow of hydraulic fluid to said hydraulic motor and said hydraulic cylinder thereby controlling the rates at which said slow opening valve and said quick opening valve are opened.

4. An automatic boiler blowdown system comprising a quick opening valve, a slow opening valve, means con meeting said quick opening valve and said slow opening valve in series in the blow down line of the boiler to be blown down, a hydraulic motor mechanically connected to said slow acting valve for opening and closing said slow opening valve, a hydraulic cylinder connected to open said quick opening valve, a hydraulic system for actuating said valves, said hydraulic system including a hydraulic pump for producing the flow of a hydraulic fluid under pressure, a solenoid operated four-way valve for controlling the operation of said hydraulic motor, a solenoid operated three-way valve -for controlling said hydraulic cylinder, a spring biasing said quick opening valve to the normally closed position, a check valve for maintaining pressure on said hydraulic cylinder while said three-way valve is actuated, and an electronic control system including a plurality of relays for controlling the operation of said three-Way valve and said four-Way valve to sequentially open and close said quick opening valve and said slow opening valve.

5. An automatic boiler bfowdown system comprising a slow opening valve and a quick opening valve connected in series in the blowdown line of the boiler, a hydraulic motor for opening and closing said slow opening valve, a hydraulic cylinder connected to open said quick opening valve, a hydraulic system including a pump for producing the flow of hydraulic fluid to drive said motor and said cylinder, said hydraulic system further including a solenoid operated 4-way valve for controlling the flow of said hydraulic fluid through said motor to open and close said slow opening valve and a solenoid operated 3-way valve for controlling the flow of said hydraulic fluid into said cylindcr to open said quick opening valve, timer means to actuatc the blo wdovvn system at predetermined intervals of time, means effective responsive to said timer means for actuating said pump and said solenoid operated 3-way valve to cause said hydraulic cylinder to open said quick opening valve, check valve means for maintaining pressure in said cylinder when said solenoid operated 3-way valve is actuated, means responsive to the opening of said quick opening valve to actuate said solenoid operated 4- way valve to control the flow of hydraulic fluid through said motor in a direction to open said slow opening valve, means responsive to the opening of said slow opening valve to stop the flow of hydraulic fluid through said motor, means effective after a predetermined interval of time to cause hydraulic fluid to flow through said motor in a direction to close said slow opening valve, means effective responsive to the closure of said slow opening valve to deactuate said pump and said solenoid operated 3-way valve, and means to close said quick acting valve when said solenoid operated 3-way valve is deactuated.

6. An automatic boiler blowdown system comprising a first valve and a second valve, means connecting said first valve and a second valve in series in the blowdown line of a boiler, first operating means effective to open and to close said first valve, second operating means effective to open and to close said second valve, and control means effective to control said first operating means and said second operating means, said control means including a timer, said timer being capable of being set to initiate a blowdown cycle at desired times, first relay means effective responsive to said timer to control said first operating means to open said first valve, means effective responsive to said first valve being in the open condition to control said second operating means to open said second valve, second relay means effective after a predetermined time delay to control said second operating means to close said second valve, means including a relay to actuate said second relay means responsive to said second valve being in the open condition, and means effective responsive to said second valve returning to the closed condition to control said first operating means to close said first valve.

7. A system as defined in claim 6 wherein said first valve is of the quick opening type, said first operating means comprising a hydraulic cylinder, means connecting said hydraulic cylinder to open said first valve, a threeway valve, means connecting said three-way valve to operate said hydraulic cylinder, a spring, and means connecting said spring to close said first valve, said control means being effective to control said three-way valve.

8. A system as defined in claim 6 wherein said second valve is one of the slow opening type, said second operating means comprising a hydraulic motor, means connecting said motor to operate said second valve, a four-way valve, and means connecting said four-way valve to operate said motor, said control means being effective to control said four-way valve to operate said motor to open said second valve and to close said second valve.

9. A system as defined in claim 6 wherein said means effective responsive to said first valve comprises a first limit switch and means connecting said first limit switch to be actuated responsive to the opening of said first valve, and wherein said means including a relay further includes a second limit switch and means connecting said second limit switch to close responsive to the opening of said second valve.

References Cited in the file of this patent UNITED STATES PATENTS 1,572,911 Wilson Feb. 16, 1926 1,739,787 Doughty et al. Dec. 17, 1929 1,853,096 Stukenborg Apr. 12, 1932 1,898,209 Parker Feb. 21, 1933 1,971,816 Hecht et al Aug. 28, 1934 1,999,439 Braun Apr. 30, 1935 2,063,122 Richardson Dec. 8, 1936 2,245,553 Biedermann et a1. June 17, 1941 2,317,546 McG-rath et al. Apr. '27, 1943 2,597,597 Rice May 20-, 1952 2,921,593 McKay Jan. 19,1960 

1. AN AUTOMATIC BOILER BLOWDOWN SYSTEM COMPRISING A SLOW OPENING VALVE, A QUICK OPENING VALVE, MEANS CONNECTING SAID QUICK OPENING VALVE AND SAID SLOW OPENING VALVE IN SERIES IN THE BLOW DOWN LINE OF THE BOILER, MEANS BIASING SAID QUICK OPENING VALVE IN A NORMALLY CLOSED POSITION, A HYDRAULIC SYSTEM EFFECTIVE TO OPEN SAID SLOW OPENING VALVE AND SAID QUICK OPENING VALVE, CONTROL MEANS FOR CONTROLLING THE OPERATION OF SAID HYDRAULIC SYSTEM TO SEQUENTIALLY OPEN AND CLOSE SAID QUICK OPENING VALVE AND SAID SLOW OPENING VALVE, AND TIMER MEANS FOR PERIODICALLY ACTUATING SAID CONTROL MEANS. 